Matrix Metalloproteinases and their natural inhibitors (TIMPs) regulate the dissolution of the extracellular matrix in growth and development, inflammatory and neoplastic diseases. The objective of this project is to investigate how cells orchestrate the episodic local dissolution of extracellular matrix by the orderly expression and function of MMPs and their inhibitors. Initially our studies are aimed at determining which MMPs are involved in the degradation of a single substrate (reconstituted fibrils of type 1 collagen) by a single cell type. To address this question we are employing a variety of molecular and cell biological approaches. Specifically we are pursuing gene knock-out and replacement strategies in order to determine the function of MT1-MMP and TIMP-2 in extracellular matrix remodeling. We are addressing the same question by transfection of cells with specific enzymes, or combination of enzymes, in order to understand the enzymatic requirement for dissolution of the extracellular matrix. We are particularly interested in using these approaches to resolve the question how nascent MMPs are activated biologically by live cells. Recently, we have focused attention on a seemingly tooth-specific MMP, enamelysin, MMP-20. We are currently involved in studies aimed at determining the developmental consequences of ablation of the enamelysin gene. - matrix metalloproteinases